The objectives are to study the ionic current flow across the nerve membrane without the complication of excitation and propagation in terms of individual ion currents and to observe the effect of changes in normal internal and external environments. These environments are altered by addition of various chemical and pharmacological agents as well as by changing the ionic environment. Chemical and pharmacological agents may block the channel or alter the kinetics. Changing the ionic environment such as the substitution of sodium or potassium by various organic and other cations produces a selectivity sequence for each channel. The long range objectives are the interpretation of nerve function in terms of ion movements and the elucidations of the structures and mechanism by which the permeabilities are controlled. Standard voltage clamp techniques are employed on the following preparations: a. Myxicola giant axon; b. Squid giant axon. For many experiments on the giant axon of Myxicola the voltage clamp is under computer control. In addition, the computer provides both on and off line analysis of the data.